Timolol is a new beta blocker with cardioselective properties. A single blind controlled study was performed to assess the efficacy of timolol maleate in doses of 10 to 30 mg per day in 20 patients affected by stable angina pectoris. The patients received a placebo for a baseline period of 2 weeks, followed by 12 weeks of timolol. The number of anginal attacks dropped from 14.9 attacks per week in the baseline period to a minimum of 4.6 attacks per week in the sixth week of treatment (P less than 0.01). The number of tablets of nitroglycerin taken per week was reduced from 6.5 during the baseline period to 2.3 in the sixth week of treatment. Resting heart rate decreased from a baseline mean value of 72 beats per minute to 51.7 and 53.7 per minute at weeks 6 and 12 respectively (P less than 0.01). Blood pressure both at rest and during exercise was significantly reduced. The mean work index measured during bicycle ergometry was 127 units before treatment; it increased by 29.4 units and 36.1 units during week 6 and week 12 respectively (P less than 0.05). There was a marked symptomatic improvement in 50% of the patients. Mild fatigue was a common side effect but it disappeared following reduction of dose. We concluded that timolol maleate significantly reduces the number of anginal attacks and increases the work capacity of patients affected by stable angina pectoris